The invention relates generally to a security system.
More particularly, the invention relates to a remote-control security system, e.g., for motor vehicles and buildings.
Remote-control security systems come in many forms. The more sophisticated systems are designed to transmit messages in coded form so that an unauthorized person having a remote-control device operating at the same frequency as such a system is unable to activate the latter since he or she does not know the code employed in the system. By way of example, reference may be had to the commonly-owned U.S. Pat. No. 4,733,215 which discloses an antitheft system of the type using encoded messages.
Although a system which transmits messages in coded form provides a degree of protection against unauthorized activation of the system, such a system is not foolproof. Thus, if an unauthorized person has a remote-control device which is capable of intercepting an encoded message during transmission, storing the message and subsequently retransmitting the message, it would be possible for this person to activate the system which generates the coded message.